1. Field of the Invention
The present invention relates to a triggering method for activating a lateral velocity estimating system for occupant protection devices.
2. Description of Related Art
Data from the United States confirm the importance of passive safety in vehicle rollovers. In 1998, half of all fatal single-vehicle accidents were attributable to a rollover. Vehicle rollovers constitute approximately 20 percent of all accident events.
Conventional systems for rollover detection consider the vehicle's roll motion and its accelerations in the X, Y, and Z directions. Reliable detection of a vehicle rollover is possible on this basis, but the decision as to whether a rollover is present is not reliably made until a late point in time during the rollover. In certain instances of vehicle rollovers that are preceded by a dynamic driving maneuver, the occupant experiences large lateral accelerations. Such maneuvers can result, for example, in so-called soil-trip rollovers. In this regard, there is still potential for future occupant protection systems in terms of the triggering behavior.
Known methods are based, for example, on evaluation of a rotation rate sensor and two acceleration sensors that are integrated into a central airbag control unit. The rotation rate sensor ascertains the rotational velocity about the vehicle's longitudinal axis using the gyro principle, and the acceleration sensors additionally measure the vehicle acceleration in the transverse and vertical directions. The rotation rate is then evaluated in the main algorithm. On the one hand it is possible to detect the type of rollover using the measured values of the acceleration sensors, and on the other hand these values serve for plausibility testing. If the rotation rate algorithm detects a rollover, the safety devices are activated only if simultaneously enabled by the plausibility check.
In another known method, a timely triggering decision in the context of rollovers with a high lateral acceleration is made possible by the fact that a float angle and the lateral velocity of the vehicle are included. In one known method for expanded rollover detection, an estimate of the lateral velocity is carried out based on a yaw rate and the vehicle velocity in the longitudinal direction, taking into account the lateral acceleration; that estimate represents an indication of the vehicle's rollover probability in the context of a lateral drift into the median strip. The so-called float angle is likewise employed for determination of the lateral velocity.
It is not possible, however, to carry out a determination of the float angle over larger angle ranges and an estimate of the lateral velocity based on the ascertained float angle, as required for rollover detection, with known methods that are used, for example, in vehicle dynamics control systems, because they are suitable only for angle ranges below 10°. The reason for the narrow validity range is that a vehicle dynamics control system can no longer be successfully implemented at greater float angles.